Abstract
Chronic kidney disease (CKD) is characterized by progressive reductions in skeletal muscle function and size. The concept of muscle quality is increasingly being used to assess muscle health, although the best means of assessment remains unidentified. The use of muscle echogenicity is limited by an inability to be compared across devices. Gray level of co-occurrence matrix (GLCM), a form of image texture analysis, may provide a measure of muscle quality, robust to scanner settings. This study aimed to identify GLCM values from skeletal muscle images in CKD and investigate their association with physical performance and strength (a surrogate of muscle function). Transverse images of the rectus femoris muscle were obtained using B-mode 2D ultrasound imaging. Texture analysis (GLCM) was performed using ImageJ. Five different GLCM features were quantified: energy or angular second moment (ASM), entropy, homogeneity, or inverse difference moment (IDM), correlation, and contrast. Physical function and strength were assessed using tests of handgrip strength, sit to stand-60, gait speed, incremental shuttle walk test, and timed up-and-go. Correlation coefficients between GLCM indices were compared to each objective functional measure. A total of 90 CKD patients (age 64.6 (10.9) years, 44% male, eGFR 33.8 (15.7) mL/minutes/1.73 m2) were included. Better muscle function was largely associated with those values suggestive of greater image texture homogeneity (i.e., greater ASM, correlation, and IDM, lower entropy and contrast). Entropy showed the greatest association across all the functional assessments (r = −.177). All GLCM parameters, a form of higher-order texture analysis, were associated with muscle function, although the largest association as seen with image entropy. Image homogeneity likely indicates lower muscle infiltration of fat and fibrosis. Texture analysis may provide a novel indicator of muscle quality that is robust to changes in scanner settings. Further research is needed to substantiate our findings.
Highlights
Skeletal muscle health decreases with advancing age and several disease states, including chronic kidney disease (CKD).[1,2] This loss of skeletal muscle mass contributes to impairments in strength and physical function;[3] these adverse changes cannot be entirely accounted for by changes in muscle size
Patients, attending nephrology outpatient clinics between 2013 and 2020 at Leicester General Hospital, UK, were recruited if they had: CKD not requiring renal replacement therapy; aged ≥18; no significant co-morbidity or physical impairment contraindicative to exercise; and sufficient ability to provide informed consent. This cross-sectional study is an exploratory analysis of pooled baseline skeletal muscle ultrasound data taken from two trials conducted by our group (ExTra-CKD: ISRCTN36489137 and DIMENSION-KD: ISRCTN84422148)
Using novel Gray level of co-occurrence matrix (GLCM) texture analysis of skeletal muscle ultrasound images, we found that better muscle function was
Summary
Skeletal muscle health decreases with advancing age and several disease states, including chronic kidney disease (CKD).[1,2] This loss of skeletal muscle mass contributes to impairments in strength and physical function;[3] these adverse changes cannot be entirely accounted for by changes in muscle size. The concept of muscle quality is increasingly being used to assess skeletal muscle health. Its assessment is a challenging, yet important area of future research as it is not sufficiently defined for use in clinical practice.[4] Muscle quality may be described as the capacity to generate force relative to the mass/volume of contractile tissue (i.e., its functionality),[5] but it may be thought of in terms of the observed architecture and composition of the muscle itself. Many methods used to quantify muscle quality are either invasive (e.g., muscle biopsies), Ultrasonic Imaging 43(3)
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